1,767 research outputs found
Convergence study and optimal weight functions of an explicit particle method for the incompressible Navier--Stokes equations
To increase the reliability of simulations by particle methods for
incompressible viscous flow problems, convergence studies and improvements of
accuracy are considered for a fully explicit particle method for incompressible
Navier--Stokes equations. The explicit particle method is based on a penalty
problem, which converges theoretically to the incompressible Navier--Stokes
equations, and is discretized in space by generalized approximate operators
defined as a wider class of approximate operators than those of the smoothed
particle hydrodynamics (SPH) and moving particle semi-implicit (MPS) methods.
By considering an analytical derivation of the explicit particle method and
truncation error estimates of the generalized approximate operators, sufficient
conditions of convergence are conjectured.Under these conditions, the
convergence of the explicit particle method is confirmed by numerically
comparing errors between exact and approximate solutions. Moreover, by focusing
on the truncation errors of the generalized approximate operators, an optimal
weight function is derived by reducing the truncation errors over general
particle distributions. The effectiveness of the generalized approximate
operators with the optimal weight functions is confirmed using numerical
results of truncation errors and driven cavity flow. As an application for flow
problems with free surface effects, the explicit particle method is applied to
a dam break flow.Comment: 27 pages, 13 figure
Large-scale simulations of viscoelastic deformable multi-body systems using quadruple discrete element method on supercomputers
Contact problems among viscoelastic materials in the multibody system is one of
the challenging topics in science and many engineering applications. We have developed an effective
simulation method of combining QDEM (Quadruple Discrete Element Method) for the deformation
analysis of structures with the DEM for the collisions among structures. However, it is
still difficult to reproduce surface topography of structures because particles only set on four
nodes of tetrahedrons in our current method. In this paper, QDEMSM (QDEM with Surface
Modeling) is newly developed. Point-polygon collisions and line-line collisions are effectively
coupled with QDEM. Our improved method was validated by several simulation results; domino
simulations using the 40 pieces of shogi (= Japanese chess) were successfully carried out. It
was also found the friction forces acted on the surface critically effected on the
propagation speeds of contact forces. In parallel computing, by applying the space-filling
curve to decomposition of the computational domain, we make it possible to contain the same
number of nodes in each decomposed domain. Our parallel
simulation code achieves a good weak scalability on the TSUBAME2.5 supercomputer
Enhanced CO and soot oxidation activity over Y-doped ceriaâzirconia and ceriaâlanthana solid solutions
Y-doped ceriaâzirconia (Ce0.8Zr0.12Y0.08O2-d,
CZY) and ceriaâlanthana (Ce0.8La0.12Y0.08O2-d, CLY)
ternary oxide solid solutions were synthesized by a facile
coprecipitation method. Structural, textural, redox, and
morphological properties of the synthesized samples were
investigated by means of X-ray diffraction (XRD), inductively coupled plasma-optical emission spectroscopy (ICPâOES), Raman spectroscopy (RS), UVâvisible diffuse re-
flectance spectroscopy (UVâvis DRS), X-ray photoelectron
spectroscopy (XPS), temperature-programmed reduction
by hydrogen (H2-TPR), high resolution transmission electron microscopy (HRTEM), and BrunauerâEmmettâTeller
surface area (BET SA) techniques. The formation of
ternary oxide solid solutions was confirmed from XRD,
RS, and UVâvis DRS results. ICPâOES analysis confirmed
the elemental composition in the ternary oxide solid solutions. HRTEM images revealed irregular morphology of
the samples. RS, UVâvis DRS, and XPS results indicated
enhanced oxygen vacancies in the Y doped samples. H2-
TPR profiles confirmed a facile reduction of CZY and CLY
samples at lower temperatures. BET analysis revealed an
enhanced surface area for CZY and CLY samples than the
respective CZ and CL undoped mixed oxides. All these
factors contributed to a better CO and soot oxidation performance of CZY and CLY samples. Particularly, the CLY
sample exhibited highest catalytic activity among the various samples investigated.We gratefully acknowledge Department of Science and Technology (DST), New Delhi for financial support of
this work (SERB Scheme SB/S1/PC-106/2012). D.D. thanks the
Department of Education, Australian Government for providing Endeavour Research Fellowship
Lieb Mode in a Quasi One-Dimensional Bose-Einstein Condensate of Atoms
We calculate the dispersion relation associated with a solitary wave in a
quasi-one-dimensional Bose-Einstein condensate of atoms confined in a harmonic,
cylindrical trap in the limit of weak and strong interactions. In both cases,
the dispersion relation is linear for long wavelength excitations and
terminates at the point where the group velocity vanishes. We also calculate
the dispersion relation of sound waves in both limits of weak and strong
coupling.Comment: 4 pages, 2 ps figures, RevTe
Structures and topological transitions of hydrocarbon films on quasicrystalline surfaces
Lubricants can affect quasicrystalline coatings surfaces by modifying
commensurability of the interfaces. We report results of the first computer
simulation studies of physically adsorbed hydrocarbons on a quasicrystalline
surface: methane, propane, and benzene on decagonal Al-Ni-Co. The grand
canonical Monte Carlo method is employed, using novel Embedded Atom Method
potentials generated from it ab initio calculations, and standard hydrocarbon
interactions. The resulting adsorption isotherms and calculated structures show
the films' evolution from submonolayer to condensation. We discover the
presence and absence of the 5- to 6-fold topological transition, for benzene
and methane, respectively, in agreement with a previsouly formulated
phenomenological rule based on adsorbate-substrate size mismatch.Comment: 5 pages, 5 figure, 1 EPAPS-material.pd
A theorem on the absence of phase transitions in one-dimensional growth models with onsite periodic potentials
We rigorously prove that a wide class of one-dimensional growth models with
onsite periodic potential, such as the discrete sine-Gordon model, have no
phase transition at any temperature . The proof relies on the spectral
analysis of the transfer operator associated to the models. We show that this
operator is Hilbert-Schmidt and that its maximum eigenvalue is an analytic
function of temperature.Comment: 6 pages, no figures, submitted to J Phys A: Math Ge
Topological defects and shape of aromatic self-assembled vesicles
We show that the stacking of flat aromatic molecules on a curved surface
results in topological defects. We consider, as an example, spherical vesicles,
self-assembled from molecules with 5- and 6-thiophene cores. We predict that
the symmetry of the molecules influences the number of topological defects and
the resulting equilibrium shape.Comment: accepted as a Letter in the J. Phys. Chem.
Multi-wavelength study of the gravitational lens system RXS J1131-1231: III. Long slit spectroscopy: micro-lensing probes the QSO structure
(ABRIDGED)
Aims: We discuss and characterize micro-lensing among the 3 brightest lensed
images (A-B-C) of the gravitational lens system RXS J1131-1231 (a quadruply
imaged AGN) by means of long slit optical and NIR spectroscopy. Qualitative
constraints on the size of different emission regions are derived.
Methods: We decompose the spectra into their individual emission components
using a multi-component fitting approach. A complementary decomposition of the
spectra enables us to isolate the macro-lensed fraction of the spectra
independently of any spectral modelling.
Results: -1. The data support micro-lensing de-amplification of images A and
C. Not only is the continuum emission microlensed in those images but also a
fraction of the Broad Line emitting Region (BLR).-2. Micro-lensing of a very
broad component of MgII emission line suggests that the corresponding emission
occurs in a region more compact than the other components of the emission line.
-3. We find evidence that a large fraction of the FeII emission arises in the
outer parts of the BLR. We also find very compact emitting region in the ranges
3080-3540 A and 4630-4800 A that is likely associated with FeII. -4. The OIII
narrow emission line regions are partly spatially resolved. This enables us to
put a lower limit of 110h^{-1} pc on their intrinsic size. -5. Analysis of MgII
absorption found in the spectra indicates that the absorbing medium is
intrinsic to the quasar, has a covering factor of 20%, and is constituted of
small clouds homogeneously distributed in front of the continuum and BLRs. -6.
Two neighbour galaxies are detected at redshifts z=0.10 and z=0.289. These
galaxies are possible members of galaxy groups reported at those redshifts.Comment: Accepted by Astronomy and Astrophysics. Small modifications to match
the final versio
Structure based development of novel specific inhibitors for cathepsin L and cathepsin S in vitro and in vivo
AbstractSpecific inhibitors for cathepsin L and cathepsin S have been developed with the help of computer-graphic modeling based on the stereo-structure. The common fragment, N-(L-trans-carbamoyloxyrane-2-carbonyl)-phenylalanine-dimethylamide, is required for specific inhibition of cathepsin L. Seven novel inhibitors of the cathepsin L inhibitor Katunuma (CLIK) specifically inhibited cathepsin L at a concentration of 10â7 M in vitro, while almost no inhibition of cathepsins B, C, S and K was observed. Four of the CLIKs are stable, and showed highly selective inhibition for hepatic cathepsin L in vivo. One of the CLIK inhibitors contains an aldehyde group, and specifically inhibits cathepsin S at 10â7 M in vitro
Dynamical Effective Medium Theory for Quantum Spins and Multipoles
A dynamical effective medium theory is presented for quantum spins and higher
multipoles such as quadrupole moments. The theory is a generalization of the
spherical model approximation for the Ising model, and is accurate up to
O(1/z_n) where z_n is the number of interacting neighbors. The polarization
function is optimized under the condition that it be diagonal in site indices.
With use of auxiliary fields and path integrals, the theory is flexibly applied
to quantum spins and higher multipoles with many interacting neighbors. A
Kondo-type screening of each spin is proposed for systems with extreme quantum
fluctuations but without conduction electrons.Comment: 16 pages, 3 Postscript figure
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